It is absolutely saying "we know better than you". It's comparing a differing preference to contaminating shared food. It's attempting to paint that opinion, which actually happens to be the most common one, as despicable and able to be dismissed out of hand. This is an extremely common rhetorical technique with paternalistic types.

For what it's worth, I don't disagree with your point about outsiders needing to accept that they don't have influence within a community. I actually very much agree, but I don't think that's actually the point being argued, nor is it what I was taking exception to.